Final answer:
The primary source of human language is still a matter of speculation, and scholars rely on indirect evidence to study its origins and evolution.
Step-by-step explanation:
The primary source of human language, properly so called, is still a matter of speculation in linguistics and other fields. Due to the lack of direct evidence, scholars have to rely on indirect evidence such as the fossil record, archaeological evidence, contemporary language diversity, studies of language acquisition, and comparisons between human language and communication systems in animals.
While there are various hypotheses about the origins of language, there is little consensus on the implications and directionality of this connection.